Although sliding characteristics of polyamide resin are excellent due to its crystallinity, many investigations have been conducted from old time already in order to achieve more excellent sliding characteristics. Solid lubricants such as molybdenum disulfide, graphite and fluorine resin and liquid lubricants such as various kinds of lubricating oil and silicone oil have been investigated as main improving agents for sliding characteristics (for example, Non-Patent Document 1).
As to a solid lubricant among those improving agents for sliding characteristics, it is necessary to compound large amount of a solid lubricant when sliding characteristics are to be further improved in a resin inherently having excellent sliding characteristics such as polyamide resin. As a result, tenacity of a polyamide resin acting as abase is significantly lowered and evaluation standards of molded parts for automobiles such as heat cycle cannot be cleared. Moreover, it is not preferred from economical viewpoint because large amount of expensive solid lubricant is compounded. On the other hand, liquid lubricant can impart highly effective sliding characteristics to the resin such as engineering plastic in a relatively small amount. However, in many cases, compatibility with the resin acting as a base is bad and there are many cases wherein surface of a molded product is polluted with such a liquid lubricant. Therefore, in a product wherein sliding characteristics are improved using such a liquid lubricant, its use is limited.
Instead of compounding various kinds of lubricants as such, it has been proposed to use a polyamide resin of high viscosity wherein molecular weight of the polyamide resin is made significantly high so as to improve the mechanical characteristics and also to improve the sliding characteristics such as low friction and low abrasion (for example, Patent Documents 1 and 2). It has been also proposed that, if necessary, a low-molecular compound such as higher fatty acid, higher fatty acid ester or higher fatty acid amide is added as an improving agent for moldability.